1. Field of the Invention
The present invention relates to a control circuit for a discontinuous conduction mode power factor correction converter using harmonic modulation, and more particularly, to a control circuit for a discontinuous conduction mode power factor correction converter using harmonic modulation, which improves a power factor and an inductor current in a discontinuous conduction mode power factor correction converter by using harmonic modulation with respect to the discontinuous conduction mode power factor correction converter.
2. Description of the Related Art
A power factor correction (PFC) circuit is used for reducing harmonics on a power line. In particular, the PFC circuit includes an accessory load so that the circuit substantially appears as a pure resistive load. The purpose of the PFC circuit is to make AC voltage and current become substantially in-phase. This improves efficiency and removes the generation of harmful harmonics.
For example, the PFC circuit operates in a frequency range from tens of kHz to hundreds of kHz, and enables a wide-range variation in input power supply and load. Therefore, the PFC circuit can suppress most of harmonic distortion and have unity power factor.
A basic circuit configuration of a DC/DC converter may be classified into six basic types according to relative positions of an inductor and an active switch: a buck converter, a boost converter, a buck-boost converter, a Cuk converter, a SEPIC converter, and a Zeta converter. The boost and buck-boost circuit configurations are suitable for execution of PFC.
Since the inductor can operate in a continuous conduction mode (CCM) or a discontinuous conduction mode (DCM), high power factor correction can be achieved. In the same output power, the inductor operating in the DCM has a larger peak current than the inductor operating in the CCM. Since power becomes higher and peak current becomes larger, the switching loss of the circuit is increased.
Thus, the CCM is suitable for high power output. However, when the inductor operates in the CCM, a control circuit needs to detect a relationship of an input voltage, an inductor current, and an output voltage in real time. Therefore, the circuit becomes complicated. In addition, a switching frequency and a duty ratio of a switch need to change constantly in each cycle of an input voltage.
When it is necessary to integrate the PFC circuit and the two-stage converter in a single-stage structure, switching elements of the PFC circuit and the two-stage converter should have the same switching frequency and duty ratio.
Therefore, when the PFC circuit operates in the CCM, the PFC circuit is unsuitable for integration into the two-stage converter. On the contrary, in the buck-boost PFC converter, in case where the switching frequency and the duty ratio of the switching element are constantly maintained at each input power supply period, the PFC function can be easily achieved when the inductor operates in the DCM.